A function returning 3.14159265.
You can use PI to calculate the circumference and area of a circle. The example below calculates the circumference and area of a circle of a given radius.
10 CLS 20 INPUT "What is the radius of the circle ",rad 30 PRINT "The circumference is: ";2*PI*rad 40 PRINT "The area is: ";PI*rad*rad 50 END
PI can also be used to convert degrees to radians and radians to degrees.
However, BBC BASIC (Z80) has two functions (RAD and DEG) which perform these conversions to a higher accuracy.